The present invention relates to the field of electronics, and, more particularly, to integrated circuit packages.
Integrated circuit (IC) devices or packages are used in a wide variety of electronic applications including computers, cellular telephones, entertainment systems, etc. A typical IC package includes a chip of semiconductor material, or IC, in which active electronic devices are formed. Surrounding the IC is an encapsulating material, such as typically formed of a thermosetting or thermoplastic resin compound. To protect the IC from damage or contamination, the encapsulating material typically totally surrounds the IC.
The IC itself may be carried by a leadframe. The leadframe includes a die pad which carries the IC, finger portions which provide the electrical pins extending outwardly from the encapsulating material, and die pad support bars which extend from the die pad to the finger portions. Contact or bond pads on the surface of the IC are typically electrically connected to respective finger portions by bond wires which are surrounded by encapsulating material.
IC packaging has typically been concerned with protection and interconnects. Low cost, high volume manufacturing techniques are well established for conventional IC packaging. However, with the advent of various types of sensor, receiving, and/or transmitting circuits based on IC""s, the need has arisen to expose some or most of the surface of the IC to the ambient environment. An example of such an IC device is an electric field fingerprint sensor, such as of the type described in U.S. Pat. No. 5,963,679 to Setlak and U.S. Pat. No. 5,862,248 to Salatino et al. Such sensors are available commercially from the assignee of these patents and the present invention, AuthenTec, Inc. of Melbourne, Fla.
The Salatino et al. patent, for example, discloses several approaches for molding the opening in the encapsulating material to expose the fingerprint sensing matrix. One approach uses a frame which holds a body of removable material in its interior and which is positioned on the IC before molding. After molding the body may be removed thereby producing the opening through the encapsulating material. In another embodiment, an upper mold includes a downward protruding portion which directly contacts the IC to exclude the encapsulating material from the surface of the IC during injection molding to thereby form the opening exposing the IC.
Somewhat similar, a number of other patents disclose forming an opening in the encapsulating material from beneath the IC. Accordingly, cooling media may be circulated in the opening, such as disclosed in U.S. Pat. No. 5,687,474 to Hamzehdoost et al. Similarly, U.S. Pat. No. 5,570,272 to Variot provides a heatsink body in the opening beneath the IC. A pressure sensor is disclosed in U.S. Pat. No. 5,424,249 to Ishibashi wherein the encapsulating material is first completely formed then an opening is cut therethrough to an underlying sensing diaphragm.
Methods for packaging IC""s with an opening therein have generally been cumbersome and expensive, such as requiring specialized pre-made packaging and flexible or rigid printed circuit boards. These approaches are not well-suited to reliable, high volume, low cost manufacturing. Indeed, despite continuing significant developments, such as those described in the above noted Salatino et al. patent, a number of challenges are still presented for an IC package that exposes a portion of the IC. For example, it may be difficult to keep encapsulating material from bleeding under a mold protrusion that contacts the IC to form the opening. Preventing crush damage to the IC from foreign particles pressed between the mold and the IC also remains a challenge. Variations in the thicknesses of the IC""s, adhesive layers, leadframes, etc. as well as accommodating IC skew also remains an area of concern.
In view of the foregoing background, it is therefore an object of the invention to provide an integrated circuit package comprising an IC and encapsulating material surrounding the IC, but leaving an exposed portion, and wherein the IC package is readily manufactured.
This and other objects, features, and advantages in accordance with the present invention are provided by an integrated circuit package comprising an IC and encapsulating material surrounding the IC, with the encapsulating material having an opening therein to define an exposed portion of the IC. In one class of embodiments, in view of the manufacturing approach, vestigial portions of encapsulating material are left on the exposed portion of the IC and spaced inwardly from a periphery of the opening in the encapsulating material. This is a result of a manufacturing process using a mold protrusion to form the opening. The mold protrusion may include a bleed-through retention channel positioned inwardly from the peripheral edges of an IC-contact surface. The bleed-through retention channel collects and retains any bleed-through of the encapsulating material and prevents its spread further inwardly onto the exposed surface of the IC.
The opening in the encapsulating material may be generally rectangular. Accordingly, the vestigial portions of encapsulating material may be arranged along at least one side of an imaginary rectangle spaced inwardly from the generally rectangular opening in the encapsulating material.
In some embodiments, the IC package may further include a leadframe carrying the IC. More particularly, the leadframe may comprise a die pad, finger portions, and a plurality of die pad support bars extending between the die pad and the finger portions at the corners. The die pad may be downset below a level of the finger portions. In addition, each of the die pad support bars may be resilient deformed to accommodate the downset of the die pad.
The package may further include bond wires extending between the IC and the finger portions. These bond wires may have a desired clearance from adjacent portions of the IC and an upper surface of the encapsulating material when the die pad is downset. In other words, shaping of the bond wires is performed to account for the downset imparted during manufacturing.
To reduce stress during cooling, the die pad may have an opening therein. Further, a low stress, low modulus adhesive may be used to secure the IC to the die pad. The encapsulating material may also be a low stress encapsulating material.
In other embodiments, the IC package may include a substrate on a back surface of the IC opposite the exposed portion. This substrate may cover the back surface so that the encapsulating material does not extend onto the back surface. In slightly different terms, the substrate, such as a printed circuit board, provides protection for the back surface of the IC and becomes part of the package.
The IC may include upper surface portions with active devices formed therein. The exposed portion of the IC may comprise these upper surface portions. In some advantageous embodiments, the active devices may define a sensor, such as an electric field fingerprint sensor, for example. Other devices may be similarly packaged.